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Topic 3 Archaea
Proper.es of Archaea • No archaeal human pathogens • size is usually 0.5–5 microm in diameter • similar shapes to Bacteria/Eukarya
– Also squares and rectangles • The Cytoplasm:
– cytoplasm molecules similar to Bacteria – inclusion bodies (e.g. gas vacuoles) – singular, circular chromosomes and lack a membrane-‐bound
nucleus – Many of the DNA replica.on enzymes of Archaea “look”
like those of Eukarya – Development of histones may have been an early “branch
point event” in the evolu.on of Archaea and Eukarya. – histones form structures that DNA wraps around (dierent in
Archaea from Eukarya) • Is a tetramer wraped in 60pb length of nucleo.de
• Cytoskeletal homologues found in both other domains – Ta0583, an ac.n homolog resembles eukaryal ac.n – Some cytoskeletal proteins more closely resemble those in
bacteria • The Cell Envelope
– all Archaea possess a plasma membrane – most have a cell wall – both structures are different from their equivalents in the
other domains
The Plasma Membrane
• unique bilayer construc.on • glycerol-‐1-‐phosphate (isomer of
G3P, seen in bacteria) • phytanyl side chains (repea.ng
isoprene units) – Isoprene are repea.ng units of
five carbons. Phytanyl side chains are four units of isoprene units and are therefore 20 carbon.
• Ether linkages • monolayers in some Archaea
– phosphoglycerol molecule on both ends
– very stable, oZen seen in archaeons living in high-‐temperature
The Cell Wall and Cell Surface • composed of pseudomurein • polysaccharide, similar to
pep.doglycan – NAG and NAT (bacteria is NAG and
NAM) – beta-‐1,3 linkages: lysozyme insensi.ve
• Cell Surface – S-‐Layer
• protect against preda.on/viruses • mediate adhesion
– Cannulae • hollow glycoprotein tubes • link cells together to form a complex
network • send nutrients to and/or send signals to
neighbors
– Flagella • similar to bacteria in func.on • But, thinner and has two subunits which are added at the base
Diversity of Archaea • two major phyla
– Crenarchaeota = Extremophiles includes: • Hyperthermophiles, Thermophiles, Mesophiles, and Psychrophiles
• Acidophiles love low PH • Barophiles love high pressure
– Euryarchaeota: • Halophiles love salt • Methanoges hate oxygen
• three other phyla have been proposed – Korarchaeota (from rRNA sequencesobtained
from nonculturable microbes) – Thaumarchaeota (low temperature former
Crenarchaeota, many oxidize ammonia – Nanoarchaeota (with only one current
member: the symbio.c archaeon Nanoarchaeum equitans)
Crenarchaeota adap.on to Extremes
• tetraether lipids/lipid monolayers • modified proteins
– more alpha-‐helical regions – more salt bridges/side chaininterac.ons
– more arginine/tyrosine – less cysteine/serine
• strong chaperone protein complexes
• thermostable DNA-‐binding proteins • reverse DNA gyrase enzyme to increase DNA supercoiling
• YOU DO NOT SEE A CHANGE IN CG CONTENT IN DNA
Euryarchaeota; Halophiles • require NaCl concentra.on > 1.5M (5
to 34% salinity) • very high intracellular [K+] offsets very
high extracellular [Na+] • Poten.al for DNA denaturing
– higher GC content (stronger bonds) – Protein denaturing need highly acidic
proteins that remain more stable in high salt environments
• Phototrophic, use bacteriorhodopsin (red) to produce a PMF
Euryarchaeota; Methanogens • Mul.ple energy pathways:
– CO2 +H2 (hydrogenoclas6c means breaking down hydrogen) to produce CH4 and H2O
– Or can use Acetate (CH3CO2 -‐ which is acetoclas6c) – Or C1 (methanol -‐ methylotrophic methanogens)
• energy released can be used to fix C • strict anaerobes • Methanogen Habitats:
– Anoxic sediments • marshes/swamps, lakes, rice paddies, moist landfill
– Animal diges.ve tracts • ruminant animal rumen (canle, sheep, elk, deer, camels) • cecal animal *cecum* (horses, rabbits) • large intes.ne of monogastrals (humans, swine, dogs)
– Geothermal H2/CO2 sources – Hydrothermal vents – Ar.ficial biodegrada.on facili.es
• sewage sludge digestors – Endosymbionts of anaerobic protozoa – Termite gut symbionts
• have an electron carrier called F420 fluorescent green
Volta Experiment
Ignicoccus (Crenarchaeota) and Nanoarchaeum (Nanoarchaeota)
• Obligate parasite of the crenarchaeote, Ignicoccus
• Nanoarchaeum have no metabolic genes, only carries genes for replica.on, transcrip.on and transla.on
• Ignicoccus has a large pariplasmid where ATP is created, almost accomidates nanoarchaeum
• Nanoarchaeum can create a s-‐layer while ignicoccus can not – This could possibly provide
protec.on.